Fix invalid characters in mangling

src/dmd/dmangle.d

@@ -591,12 +591,8 @@ public:
             assert(slice.length);
             foreach (const char c; slice)
             {
-                assert(c == '_' ||
-                       c == '@' ||
-                       c == '?' ||
-                       c == '$' ||
-                       isalnum(c) ||
-                       c & 0x80);
+                assert(c.isValidMangling, "The mangled name '" ~ slice ~ "' " ~
+                    "contains an invalid character: " ~ c);
             }
         }
     }
@@ -1101,6 +1097,34 @@ public:
     }
 }
 
+/// Returns: `true` if the given character is a valid mangled character
+package bool isValidMangling(dchar c)
+{
+    return
+        c >= 'A' && c <= 'Z' ||
+        c >= 'a' && c <= 'z' ||
+        c >= '0' && c <= '9' ||
+        c != 0 && strchr("$%().:?@[]_", c);
+}
+
+// valid mangled characters
+unittest
+{
+    assert('a'.isValidMangling);
+    assert('B'.isValidMangling);
+    assert('2'.isValidMangling);
+    assert('@'.isValidMangling);
+    assert('_'.isValidMangling);
+}
+
+// invalid mangled characters
+unittest
+{
+    assert(!'-'.isValidMangling);
+    assert(!0.isValidMangling);
+    assert(!'/'.isValidMangling);
+    assert(!'\\'.isValidMangling);
+}
 
 /******************************************************************************
  * Returns exact mangled name of function.

src/dmd/dsymbolsem.d

@@ -28,6 +28,7 @@ import dmd.declaration;
 import dmd.denum;
 import dmd.dimport;
 import dmd.dinterpret;
+import dmd.dmangle;
 import dmd.dmodule;
 import dmd.dscope;
 import dmd.dstruct;
@@ -1744,7 +1745,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
                     dchar c = p[i];
                     if (c < 0x80)
                     {
-                        if (c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z' || c >= '0' && c <= '9' || c != 0 && strchr("$%().:?@[]_", c))
+                        if (c.isValidMangling)
                         {
                             ++i;
                             continue;